Pump element and piston pump for generating high fuel pressure

ABSTRACT

A pump element ( 1 ) and a piston pump for generating high fuel pressure are proposed, in which tilting of the piston base ( 15 ) relative to a drive shaft ( 5 ) is effectively suppressed, so that the service life of the high-pressure fuel pump is increased.

PRIOR ART

[0001] The invention relates to a pump element for a piston pump forgenerating high fuel pressure in fuel injection systems of internalcombustion engines, as generically defined by the preamble to claim 1,and to piston pumps in accordance with coordinate claim 12.

[0002] In nearly all types of piston pumps, the rotary motion of a driveshaft is converted into an oscillating motion of the piston of a pumpelement. In so-called internally braced radial piston pumps forgenerating high fuel pressure in fuel injection systems of internalcombustion engines, a plurality of pump elements are disposed, forinstance radially to a drive shaft supported in a pump housing. Thepistons of the pump elements are actuated by an eccentric portion of thedrive shaft or by cams of the drive shaft. Because of the high pressuresto which the fuel must be brought, the forces to be transmitted by thedrive shaft to the pistons are very high. When the rotary motion of thedrive shaft is converted into the oscillating motion of the pistons ofthe pump elements, forces between the drive shaft and the pistons occurthat also act in the circumferential direction of the drive shaft.Similar effects also occur between the drive shaft and the pistons ofin-line injection pumps or distributor injection pumps.

[0003] To reduce the wear between the pistons and the drive shaft, it isknown from German Published, Nonexamined Patent Disclosure DE-OS 198 02475 to provide a ring with flat faces, which does not rotate with thedrive shaft, on the eccentric portion of the drive shaft of a radialpiston pump. On the end of the piston toward the ring, a plate isprovided in this radial piston pump. This plate is braced against theflat faces on the ring. When the pump elements are only partly filled inpartial-load operation, the ring tends to rotate relative to the pumpelements, because of the uneven load. The result is excessive loads onboth the ring and the pump elements. These loads can lead to failure ofa pump element or of the entire high-pressure fuel pump.

[0004] The object of the invention is to furnish a pump element and apiston pump for generating high fuel pressure which is simple inconstruction and has still further-enhanced reliability under alloperating conditions.

[0005] In a pump element for a piston pump for generating high fuelpressure in fuel injection systems of internal combustion engines, withat least one piston, disposed in a cylinder bore, the piston having apiston base and a piston shaft, and with a plate, mounted on the pistonbase, for transmitting the pumping motion from a drive mechanism to thepiston, the piston base having a bearing face cooperating with anindentation in the plate, this object is attained according to theinvention in that the bearing face and the indentation form anessentially plane contact zone.

ADVANTAGES OF THE INVENTION

[0006] Because of the plane contact zone between the bearing face andthe indentation, it is possible for the forces to be transmitted in theaxial direction of the piston to be transmitted uniformly over a largearea. Also because of the plane piston shaft, it can be prevented thatthe plate will execute a tilting motion, which is caused or madepossible by the reciprocating motions in the tangential direction of thering supported on the drive shaft. It is attained as a result that underall operating states of the high-pressure fuel pump, the ring willexecute no rotary motion at all, or only a very slight rotary motion,and thus the bending stress on the plate and the piston is reduced. Thisis significant above all when the pump elements are not pumping the fullpumping quantity but instead are only partly filled because ofcorresponding throttling of the fuel inflow. When the pump elements arepartly filled, vapor bubble formation occurs in the pump elements,resulting in a nonuniform transmission of torque from the drive shaft tothe pump elements. As a consequence, the ring tends to execute theaforementioned unwanted rotary motions. The embodiment of the pumpelements according to the invention suppresses the rotary motions of thering to such an extent that point-type excessive stresses on the pumpelement or the ring no longer occur. As a result, the service life ofthe pump elements and of the overall piston pump is increased without anincrease in production costs.

[0007] It is especially advantageous if the contact zone is larger thanor equal to the cross-sectional area of the piston shaft, so that theunwanted tilting of the plate and the unwanted rotary motion of the ringare reduced further.

[0008] To enable compensating for slight imprecisions in production orskewed positions of the longitudinal axis of the pistons relative to thelongitudinal axis of the drive shaft, it can furthermore be providedthat the bearing face or the face of the indentation that together withthe bearing face forms the contact zone is curved, with a radius greaterthan 20× the diameter of the piston shaft. With this large radius ofcurvature, it is assured that production variations can be compensatedfor, without enabling tilting of the plates or a rotary motion of thering.

[0009] In a further feature of the invention, it is provided that thepiston base and the plate are joined together by positive engagement bymeans of a plate holder, which prevents damage to these components andmakes it easier to form a load-bearing film of lubricant.

[0010] In a further advantageous feature of the invention, the pistonbase has a collar, and that the plate holder is joined to the piston viathe collar, so that on the one hand, a large contact zone between theplate and the piston base becomes possible, and on the other, amore-secure positive engagement between the piston and the plate holderis assured. This version is also easy to assemble, since the number ofcomponents is very low.

[0011] Alternatively, the piston base can also have a groove with a snapring, and that the plate holder is braced on the snap ring, so that theproduction of the piston is simplified still further.

[0012] In further features of the invention, it can be provided that theplate holder is joined to the plate by creative forming, in particularby crimping or folding, so that a durably loadable connection of theplate holder and the plate is established in a simple and effective way.

[0013] To make assembly easier, the plate, on its circumference on theside toward the piston, can have a chamfer.

[0014] An especially secure connection between the plate holder and theplate can be attained if the plate has a collar, and that the plateholder surrounds the collar.

[0015] Alternatively, the plate can also be joined directly to thepiston, in particular by crimping or folding. In this variantembodiment, the number of components is reduced still further, which hasa positive effect on the production costs.

[0016] It has also proved to be advantageous if a crimped edge isembodied on the plate, and the crimped edge engages the groove of thepiston or surrounds the collar of the piston, since in these exemplaryembodiments the aforementioned advantages also come into play.

[0017] In a piston pump for generating high fuel pressure in fuelinjection systems of internal combustion engines, in particular in acommon rail injection system, having at least one pump element, theobject stated above is also attained in that the at least one pumpelement is a pump element of one of the foregoing claims. In this pistonpump, the advantages of the invention come fully into play. Inparticular, it has proved to be advantageous to embody the piston pumpof the invention as a radial piston pump, in accordance with claim 13 orclaim 14.

[0018] Further advantages and advantageous features of the invention canbe learned from the ensuing drawings, their description, and the claims.

DRAWING

[0019] Shown are:

[0020]FIG. 1, a cross section through one exemplary embodiment, embodiedas a radial piston pump, of a high-pressure fuel pump of the invention;

[0021]FIG. 2, a more-detailed illustration of the first exemplaryembodiment of a pump element of the invention;

[0022] FIGS. 3-5, a second exemplary embodiment of a pump element of theinvention; and

[0023] FIGS. 6-7, a cross section and a plan view on a third exemplaryembodiment of a plate of the invention.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0024] In FIG. 1, a section is shown through a radial piston pump,equipped with pump elements 1 of the invention, for generating high fuelpressure in injection systems of internal combustion engines.

[0025] In this radial piston pump, identified overall by referencenumeral 3, there are three pump elements 1, disposed at an angle of 120°each from one another, about a drive shaft 5. In the sectional plane ofFIG. 1, an eccentric portion of the drive shaft 5 is shown. Above andbelow the plane of the drawing, the drive shaft 5 is rotatably supported(not shown) in a housing 7 of the radial piston pump 3.

[0026] A pump element 1 comprises a cylinder bore 9 and a piston 11,which is guided sealingly in the cylinder bore 9. The piston 11 in turncomprises a piston shaft 13 and a piston base 15. A plate 17 is securedto the piston base 15.

[0027] A ring 19 with flat faces 21 is disposed between the eccentricportion of the drive shaft 5 shown in FIG. 1 and the plates 17. Thispolygonal ring 19 serves to convert the rotary motion of the eccentricportion of the drive shaft 5 into an oscillating motion. During arotation of the eccentric portion of the drive shaft 5, the polygonalring 19 oscillates, both in the direction of the longitudinal axis ofthe pistons 11 and perpendicular to the longitudinal axis of the pistons11. The polygonal ring 19 should not rotate in this process. Thiscreates a sliding motion between the plate 17 and the flat face 21. Atilting moment on the plate 17 results from this sliding motion.

[0028] If the pumping chambers 23 of the pump elements, disposed abovethe pistons 11, are only partly filled with fuel (not shown) inpartial-load operation of the radial piston pump 3, the powertransmitted from the drive shaft 5 to the pump elements 1 via the ring19 is not uniform. As a consequence, the polygonal ring 19 tends torotate somewhat in the direction of rotation of the drive shaft 5. Thisresults in a considerable bending moment on the plates 17. Because ofthe embodiment according to the invention of the piston base 15 and theplates 17, it is possible to suppress this unwanted rotary motion of thepolygonal ring 19 in all operating states, or to reduce it to such anextent that it no longer adversely affects the service life of theradial piston pump 3 or its pump elements 1. In the drawings thatfollow, exemplary embodiments of pump elements of the invention areshown and will be described below.

[0029] In FIG. 2, a detail of a first exemplary embodiment of a pumpelement 1 of the invention is shown in cross section. In this exemplaryembodiment, a groove 25 has been punched into the piston base 15, and asnap ring 27 is placed in the groove 25.

[0030] The piston base has an essentially plane bearing face 29, whichprotrudes into an indentation 31 in the plate 17. The bearing face 29 ofthe piston base 15 rests on the bottom 33 of the indentation 31. Theresult is an essentially plane contact zone between the bearing face 29and the indentation 31, that is, the bottom 33 of the indentation 31.

[0031] The contact zone (not identified by reference numeral in FIG. 2),in the first exemplary embodiment, is as large as the cross section ofthe piston shaft 13, so that a very good introduction of the forces inthe axial direction of the piston shaft, which are transmitted from theplate 17 to the piston base 15, exists. Moreover, the plane contact zoneprevents the plate 17 from being to tilt relative to the piston shaft13. As a consequence, the above-described rotary motion of the polygonalring 19 (see FIG. 1) in partial-load operation of the radial piston pump3 is also effectively suppressed, and a plane contact zone always existsbetween the piston base 15 and the plate 17 on the one hand, and betweenthe plate 17 and the flat faces 21 of the polygonal ring 19, on theother. Hence point-type excessive stress on the flat faces 21, the plate17, or the piston base 15 does not occur. The result is an increasedservice life of the radial piston pump 3.

[0032] In order that the piston shaft 13, after reaching its top deadcenter (not shown) will be moved back to bottom dead center (not shown),a plate holder 35 is provided, which in an opening 37 receives thepiston shaft 13. By means of the snap ring 27, a force from the plateholder 35 in the direction of the piston base 15 can be transmitted tothe piston shaft 13. A compression spring 39, which is braced on one endon the pump holder 35 and on the other on the housing 7 of the radialpiston pump 3 (see FIG. 1), presses the plate holder 35 from top deadcenter to bottom dead center when the eccentric portion of the driveshaft 5 (see FIG. 1) executes the corresponding rotary motion. Via thesnap ring 27, this motion is also transmitted to the piston shaft 13. Sothat the plate 17 will not be able to come loose from the piston base15, the plate holder 35 also has a crimped edge 39, which surrounds acollar 41 of the plate 17. The exemplary embodiment shown in FIG. 2 isvery simple to produce, since the piston shaft 13 and the piston base 15have the same diameter and can thus be ground in the same chuck. Toenable compensating for slight errors of alignment between the cylinderbore 9 and the pivot axis of the drive shaft 5 (not shown), it can beprovided that either the bearing face 29 or the bottom 33 of theindentation 31 is slightly curved. It has proved to be advantageous ifthe radius of curvature is greater than 20× the diameter of the pistonshaft 13. In that case, a plane contact zone between the bearing face 29and the bottom 33 is still achieved, yet point-type excessive stressesdo not occur.

[0033] On the bearing face 29, which comes into contact with the ring19, not shown in FIG. 5, the plate 17 has a chamfer 40. The effect ofthe chamfer 40 is that even if rotation of the polygonal ring 19, notshown, should occur under unfavorable conditions, the plate holder 35will not be damaged by the resultant tilting motion of the plate 17. Thechamfer 40 can be provided in all the exemplary embodiments of the pumpelement 1 of the invention.

[0034] In FIG. 3, a piston 11 of a second exemplary embodiment of a pumpelement of the invention is shown. In this exemplary embodiment, thepiston base 15 adjoining the piston shaft 13 has a markedly largerdiameter than the piston shaft 13. It is attained as a result that thepiston base 15 has a collar 43. Because of the collar 43, the bearingface 29 of the piston base 15 is enlarged. In this exemplary embodiment,the bearing face 29 is embodied as slightly curved.

[0035] In FIG. 4, a plate 17 that belongs to the piston 11 of FIG. 3 isshown. The indentation 31 is dimensioned such that the piston base 15fits precisely into the indentation 31.

[0036] In FIG. 5, the piston 11 and the plate 17 of FIGS. 3 and 4 areshown in the assembled state. In this exemplary embodiment, the plateholder 35 transmits the force, exerted on it by the spring 38, onto thepiston shaft 13 via the collar 43. As a result, the groove 25 and thesnap ring 27 (see FIG. 2) can be omitted. It is immediately clear fromFIG. 5 that the contact zone between the piston base 15 and the plate 17is larger than in the first exemplary embodiment. As a consequence, theload per unit of surface area between the piston base 15 and the bottom33 of the indentation 31 in the plate 17 is reduced further. Moreover,the rotation of the polygonal ring 19 (see FIG. 1) can be suppressedeven more effectively.

[0037] For centering the spring 38, the plate holder 35 has first lugs36 a, which are curved upward. In alternation with the first lugs 36 a,the plate holder 35 has second lugs 36 b, which are curved downward. Theplate 17 is fixed to the piston base 15 by the second lugs 36 b.

[0038] On the bearing face 29, which comes into contact with the ring19, not shown in FIG. 5, the plate 17 has a chamfer 40. The effect ofthe chamfer 40 is that even if rotation of the polygonal ring 19, notshown, should occur under unfavorable conditions, the plate holder 35will not be damaged by the resultant tilting motion of the plate 17. Thechamfer 40 can be provided in all the exemplary embodiments of the pumpelement 1 of the invention.

[0039] In FIGS. 6 and 7, a plate 17 of a third exemplary embodiment of apump element of the invention is shown in cross section and in planview. In this exemplary embodiment, no plate holder is provided. Therequisite positive-engagement connection between the piston shaft 13(not shown) and the plate 17 is established via a crimped edge 45. Ifthe piston base 15 of a piston 11, not shown, has been introduced intothe indentation 31 of the plate 17, the crimped edge 45 is bent overinward and pressed into a groove in the piston 11, not shown. The grooveand the crimped edge 45 must be dimensioned such that in all cases thepiston base 15 (not shown) will rest on the bottom 33 of the indentation31. To make it crimping the crimped edge 45 inward easier, recesses 47are provided in the crimped edge 45.

[0040] The above-described exemplary embodiments of pump elements arenot limited to radial piston pumps, but instead can also be used inin-line or distributor injection pumps.

1. A pump element for a piston pump (3) for generating high fuelpressure in fuel injection systems of internal combustion engines, withat least one piston (11), disposed in a cylinder bore (9), the piston(11) having a piston base (15) and a piston shaft (13), and with a plate(17), mounted on the piston base (15), for transmitting the pumpingmotion from a drive mechanism (5) to the piston (11), the piston base(15) having a bearing face (29) cooperating with an indentation (31) inthe plate (17), characterized in that the bearing face (29) and theindentation (31) form an essentially plane contact zone ( ).
 2. The pumpelement of claim 1, characterized in that the contact zone ( ) is largerthan or equal to the cross-sectional area of the piston shaft (13). 3.The pump element of claim 1 or 2, characterized in that the bearing face(29) or the face ( ) of the indentation that together with the bearingface (29) forms the contact zone ( ) is curved, with a radius greaterthan 20× the diameter of the piston shaft (13).
 4. The pump element ofone of the foregoing claims, characterized in that the piston base (15)and the plate (17) are joined together by positive engagement by meansof a plate holder (35).
 5. The pump element of claim 4, characterized inthat the piston base (15) has a collar (43), and that the plate holder(35) is joined to the piston (11) via the collar (43).
 6. The pumpelement of claim 4, characterized in that the piston base (15) has agroove (25) with a snap ring (27), and that the plate holder (35) isbraced on the snap ring (27).
 7. The pump element of one of claims 4-6,characterized in that the plate holder (35) is joined to the plate (17)by creative forming, in particular by crimping or folding.
 8. The pumpelement of one of claims 4-7, characterized in that the plate (17), onits circumference on the side toward the piston (11), has a chamfer ( ).9. The radial piston pump of one of claims 4-8, characterized in thatthe plate (17) has a collar (41), and that the plate holder (35)surrounds the collar (41).
 10. The pump element of one of the foregoingclaims, characterized in that the plate (17), on its bearing faceoriented toward the polygonal ring (19), has a chamfer (40).
 11. Thepump element of claim 10, characterized in that a crimped edge (45) isembodied on the plate (17), and that the crimped edge (45) engages thegroove (25) of the piston (11) or surrounds the collar (43) of thepiston (11).
 12. A piston pump for generating high fuel pressure in fuelinjection systems of internal combustion engines, in particular in acommon rail injection system, having at least one pump element (1),characterized in that the at least one pump element (1) is a pumpelement (1) of one of the foregoing claims.
 13. The piston pump of claim12, characterized in that the piston pump is embodied as a radial pistonpump.
 14. The piston pump of claim 10, characterized in that the pistonpump as a radial piston pump with a drive shaft (5) supported in a pumphousing (7), which shaft is embodied eccentrically, and with preferablya plurality of pump elements (1) disposed radially relative to the driveshaft (5), and the pistons (11) are movable radially back and forth inthe respective cylinder chamber ( ) by rotation of the drive shaft (5),and a ring (27) with flat faces (21) is disposed between the drive shaftand the plate (17).
 15. The piston pump of claim 12, characterized inthat the piston pump is embodied as a distributor pump or in-line pump.